The present invention pertains to wrenches.
Wrenches, such as socket wrenches and box wrenches, have long been made with their inner corners shaped as rounded recesses to reduce the risk of cracks at the corners, where the thickness is small and the corners cause stress concentrations. Examples of this are described in U.S. Pat. Nos. 3,125,910, 3,273,430 and 4,581,957. Wrenches of these types are commonly used in mechanical power wrenches which often have an impact function when a preselected static torque value is exceeded. The stresses during the impacts can then reach high values and cause fatigue cracks in the wrenches if the corners are not rounded enough.
It is desirable that it be possible to use the wrench for nuts with worn or otherwise slightly differing profile. In that case it is important that the corners of the nut do not become overstressed and deformed, which is achieved by leaving them free of contact in the corner recesses. It is also desirable to avoid having sharp edges of the recesses cut into the surface of the nut, damaging the rust protection. This may be avoided by making the surface of the wrench slightly sloping as in U.S. Pat. No. 3,273,430, fully rounded as in U.S. Pat. No. 3,125,910, or both as in U.S. Pat. No. 4,581,957. One result of this is, however, that nuts with already deformed corners will be contacted near the center of the hexagon side, causing a reduced leverage and very large radial forces which may damage the wrench. It will also make the rotational contact very elastic, which will partly cancel the effect of the impact function.
The present invention concerns a type of socket wrenches, box wrenches or other fixed wrenches which reduces the stress concentration at the corners, and which will make a well defined contact far enough from the corners and from the rotation center, even when turning deformed nuts.